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Actinobacteria of Magnesite Mines Habitat: Diversity, Siderophore Production and Its Antagonistic Potential

Abstract

The magnesite mines habitats in the world can be considered as an inexhaustible resource for biotechnology that has not been well exploited. In the present study, eight soil samples were collected from magnesite mines located in Chalk Hills region of Salem, South India for the isolation of actinobacteria. Actinobacterial count of magnesite soil ranged from 3.0 to 16 x 103 cfu/g of dry soil. Fifteen actinobacterial strains were selected from the total isolates based on their cultural characteristics and were screened for siderophore production, antibacterial activity and enzyme activity. All actinobacterial isolates produced siderophores in Iron free succinate agar medium (pH 8.0) as evidenced by positive reaction in O-CAS assay. Among the actinobacterial isolates tested for antagonism, strain A-6 showed broad spectrum of activity against test bacterial pathogens. Screening for enzyme activity revealed that 100% of isolates showed amylase and L-glutaminase activity, followed by 93.33% L-asparaginase and protease, 66.66% cellulase, and 46.66% lipase activity. Detection of chemical nature of siderophore produced by all the actinobacterial strains revealed them as carboxylates. Quantitative estimation of siderophores by CAS shuttle assay revealed the yield of 10% to 73% siderophore units. Studies carried out in-vitro revealed that the antibacterial activity of crude siderophore obtained from the potent actinobacterial strain A-6 was by way of chelation of iron resulting in its unavailability to the test bacterial pathogens. Based on phenotypic characteristics and 16s rRNA gene sequence analysis the potent actinobacterial strain A-6 has been identified as Streptomyces mutabilis. Phylogenetic tree was made by neighbor-joining method. The present study is the first report on carboxylate type of siderophore production in actinobacteria isolated from Indian magnesite mines. The in-vitro antagonistic action of siderophores of Streptomyces mutabilis has given a new focus of attempts to exploit the siderophore systems for the treatment of human infections.

Chandrasekaran Swaminathan, Ramasamy Balagurunathan

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